Is aerodynamic lift ever useful in rocket flight?

Question

When a rocket is traveling through an atmosphere, the component of the aerodynamic force in the direction of motion is called drag, and the component perpendicular to that is called lift. Usually a rocket is pointed in nearly the same direction as motion, but not necessarily exactly. See the NASA illustration below.

For simulation, and for flight guidance and control, consideration of lift is essential. Lift is therefore important.

My question though: is lift ever useful when rockets are traveling in an atmosphere?

And here, I mean "rocket-shaped" rockets; not car-shaped, or plane-shaped rockets, but the long, approximately cylindrically symmetric ones that tend to fly from low altitudes up into space. (yes, and more frequently these days, back down again).

Image from https://spaceflightsystems.grc.nasa.gov/education/rocket/rktstab.html

Answer 1

Angling to get lift is going to increase the atmospheric cross-section of the rocket and so increase drag. For any reasonable angle of attack, the drag force is going to be much larger than the lift force, so I believe that for powered ascent it makes the most sense to minimize drag, which means zero AoA and zero lift. This also, as Mark Adler notes, minimizes lateral stresses on the vehicle, allowing structural weight to be minimized.

Note that the total drag losses on a large rocket in ascent to LEO are small -- for Saturn V, about 0.5% of the total ∆v expenditure. Since low-AoA lift is a small fraction of drag, any gain from body lift would be extremely small.

Of course, there have to be minor excursions from zero AoA during a powered ascent (though hopefully only small ones); these should be positive AoA in order to take advantage of what little lift there is.

That said, lift is useful for steering during unpowered flight; the Falcon 9 first stage uses body lift to control its downrange flight to an ASDS. It's also very important for control of reentry vehicles, but those aren't "rocket-shaped rockets" so they're outside of the scope of your question.

Answer 2

As far as I know, no. In order to make a cylindrical rocket as light as possible, they are flown to minimize the side loads to the structure -- as close to a zero angle of attack as possible. If they wanted to use lift, it would increase the mass of the structure to be able to take substantial drag forces from the side. There would not be sufficient benefit from the lift of a cylindrical structure to offset that mass increase.

Wings or other lifting surfaces on the other hand (which you are ruling out), could potentially provide some benefit in the early parts of ascent. That was the case for Pegasus.

Answer 3

You said it yourself, Lift is important for guidance and control. As a matter of fact a rocket is designed in such a way, that the center of pressure is aft of the center of gravity. The distance between CG and CP is also called the caliber stability margin measured in rocket caliber.

You can use the fins of a rocket to control the direction and magnitude of the lift force and therefore change the positon of the center of pressure and therefore the stability of your rocket in the atmosphere.

Hence, yes, lift is useful.

Answer 4

Yes lift is useful and helpful to rockets even those going to space. The angle of attack thru the air causes lift that can help reduce gravity losses. The control systems automatically adjust the angle of attack to follow the chosen flight path thereby accounting for lift and drag.

Aircraft rely almost completely on lift to overcome gravity - rockets attempt to get to orbit fast to reduce drag and gravity losses but a little help from the atmosphere is welcome - they have to overcome drag so they may as well try to generate some lift to compensate. The rocket shape matters here as some shapes have a better lift to drag ratio - something like the Saturn 5 is not as good as a smoothly curved design with a ballistic shape. I expect the aerodynamic lift that is attainable is quite low and cost of drag is high so space rockets are optimised to reduce drag and gravity losses instead of optimising for aerodynamic lift/drag ratio as an aircraft would. The Northrop Grumman Pegasus first stage has a small wing like an aircraft to provide some extra lift on the first stage. A vehicle like starship which has drag flaps will get some extra drag and lift from these features during the short period that the rocket remains in the atmosphere as it performs it's gravity turn.